It has been well established in the prior art that hydrocarbon oils possessing superior properties in applications such as low viscosity lubricants, insulating fluids for electrical transformers, additives for lubricants, and the like can be prepared by alkylation of aromatic compounds using using higher molecular weight olefins and olefinic oligomers.
Pellegrini, Jr. U.S. Pat. No. 4,238,343 discloses a synthetic oil composition useful as an insulating fluid in electrical apparatus comprising the mono or di-alkylation product from the alkylation of aromatics with oligomers containing at least 30 and up to 60 carbon atoms. The oligomers are prepared by Lewis acid catalysis by methods well known in the art. The alkylation reaction is conducted using conventional liquid Lewis acid catalyst and the degree of substitution is controlled by the aromatic to olefin mole ratio. Dimers are separated from oligomers and not included in the alkylation reaction.
Dressler et al. U.S. Pat. No. 4,604,491 discloses a synthetic oil composition for functional fluids such as lubricants, heat transfer fluids, vacuum pump oils, etc. The compositions comprise mono and polyalkylated naphthalenes prepared by the alkylation of naphthalene with alpha-olefins in contact with high silica zeolites. The alkyl substituent on naphthalene contains between 12 and 26 carbon atoms.
Yoshida et al. U.S. Pat. No. 4,714,794 discloses a synthetic oil composition comprising monoalkylated naphthalene obtained by alkylation of naphthalene with alkyl halide, alcohol or a straight chain mono-olefin having six to twenty four carbon atoms. The mole ratio of alpha to beta substitution on naphthalene is at least 1.0. The products exhibit high oxidation stability.
Recently, novel lubricant compositions (referred to herein as HVI-PAO) comprising polyalpha-olefins and methods for their preparation employing as catalyst reduced chromium on a silica support have been disclosed in U.S. patent applications Ser. No. 210,434 and 210,435 filed June 23, 1988, incorporated herein by reference. The process comprises contacting C.sub.6 -C.sub.20 1-alkene feedstock with reduced valence state chromium oxide catalyst on porous silica support under oligomerizing conditions in an oligomerization zone whereby high viscosity, high VI liquid hydrocarbon lubricant is produced having branch ratios less than 0.19 and pour point below -15.degree. C. The process is distinctive in that little isomerization of the olefinic bond occurs compared to known oligomerization methods to produce polyalpha-olefins using Lewis acid catalyst. Lubricants produced by the process cover the full range of lubricant viscosities and exhibit a remarkably high viscosity index (VI) and low pour point even at high viscosity. The assynthesized HVI-PAO oligomer has a preponderance of terminal olefinic unsaturation.
In the preparation of the novel HVI-PAO lubricant, alpha-olefin dimer containing olefinic unsaturation can be separated from the oligomerization reaction. The composition of the dimer mixture conforms to the unique specificity of the oligomerization reaction in that little double bond isomerization is found and shows a low branch ratio.
According, it is an object of the present invention to provide a process for the alkylation of aromatic hydrocarbons using HVI-PAO olefinic dimer.
Yet another object of the present invention is to provide a process for the monoalkylation of aromatic hydrocarbons with HVI-PAO dimer.
A further object of the present invention is to provide a method for increasing the thermal stability of lubricant compositions using monoalkylated aromatics derived from HVI-PAO dimer.